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<html>

<head>
  <meta charset='utf-8'>
  <meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'>
  <meta name='mobile-web-app-capable' content='yes'>
  <meta name='apple-mobile-web-app-capable' content='yes'>
  <link rel='icon' type='image/png' sizes='32x32' href='../favicon-32x32.png'>
  <link rel='icon' type='image/png' sizes='96x96' href='../favicon-96x96.png'>
  <link rel='stylesheet' href='../css/common.css'>

  <title>Projection Layer</title>
</head>

<body>
  <header style="max-width: 800px;">
    <details open>
      <summary>Projection Layer</summary>
      <p>
        This sample shows how to draw a scene into a projection layer.
        Projection layers are used for rendering interactive/constantly
        changing elements that need to be redrawn every frame, like
        controllers or menu systems/other UI elements.
        <a class="back" href="./index.html">Back</a>
      </p>
      <input type="checkbox" id="texture-array">Use Texture Array</input>
    </details>
  </header>
  <main style='text-align: center;'>
    <p>Click 'Enter VR' to see content</p>
  </main>
  <script type="module">
    import { WebXRButton } from '../js/util/webxr-button.js';
    import { Scene, WebXRView } from '../js/render/scenes/scene.js';
    import { Renderer, createWebGLContext } from '../js/render/core/renderer.js';
    import { Gltf2Node } from '../js/render/nodes/gltf2.js';
    import { SkyboxNode } from '../js/render/nodes/skybox.js';
    import { QueryArgs } from '../js/util/query-args.js';

    // If requested, use the polyfill to provide support for mobile devices
    // and devices which only support WebVR.
    import WebXRPolyfill from '../js/third-party/webxr-polyfill/build/webxr-polyfill.module.js';
    if (QueryArgs.getBool('usePolyfill', true)) {
      let polyfill = new WebXRPolyfill();
    }

    // XR globals.
    let textureArrayCheck = document.getElementById('texture-array');
    let xrButton = null;
    let xrSession = null;
    let xrRefSpace = null;
    let xrGLFactory = null;
    let xrFramebuffer = null;

    // WebGL scene globals.
    let gl = null;
    let renderer = null;
    let scene = new Scene();
    scene.addNode(new Gltf2Node({ url: '../media/gltf/space/space.gltf' }));
    scene.addNode(new SkyboxNode({ url: '../media/textures/milky-way-4k.png' }));

    // Layer globals
    let proj_layer = null;
    let usingTextureArray = false;

    function initXR() {
      xrButton = new WebXRButton({
        onRequestSession: onRequestSession,
        onEndSession: onEndSession
      });
      document.querySelector('header').appendChild(xrButton.domElement);

      if (navigator.xr) {
        navigator.xr.isSessionSupported('immersive-vr').then((supported) => {
          xrButton.enabled = supported;
        });
      }
    }

    function onRequestSession() {
      if (!xrSession) {
        // Unlike all other layer types, use of a single projection layer does
        // not require the 'layers' feature.
        navigator.xr.requestSession('immersive-vr').then(onSessionStarted);
      } else {
        onEndSession();
      }
    }

    function initGL() {
      if (gl) { return; }

      // Create a WebGL context to render with, initialized to be compatible
      // with the XRDisplay we're presenting to.
      gl = createWebGLContext({ xrCompatible: true, webgl2: true, });
      document.body.appendChild(gl.canvas);
      gl.clearColor(0.8, 0.8, 0.8, 1);

      function onResize() {
        gl.canvas.width = gl.canvas.clientWidth * window.devicePixelRatio;
        gl.canvas.height = gl.canvas.clientHeight * window.devicePixelRatio;
      }
      window.addEventListener('resize', onResize);
      onResize();

      renderer = new Renderer(gl);
      scene.setRenderer(renderer);
    }

    // Called when we've successfully acquired a XRSession. In response we
    // will set up the necessary session state and kick off the frame loop.
    function onSessionStarted(session) {
      xrSession = session;

      // This informs the 'Enter XR' button that the session has started and
      // that it should display 'Exit XR' instead.
      xrButton.setSession(session);

      // Render correct controller models if supported by WebXR input profile
      scene.inputRenderer.useProfileControllerMeshes(session);

      // Listen for the sessions 'end' event so we can respond if the user
      // or UA ends the session for any reason.
      session.addEventListener('end', onSessionEnded);

      initGL();

      xrFramebuffer = gl.createFramebuffer();
      xrGLFactory = new XRWebGLBinding(session, gl);

      session.requestReferenceSpace('local').then((refSpace) => {
        xrRefSpace = refSpace;
        usingTextureArray = textureArrayCheck.checked;
        proj_layer = xrGLFactory.createProjectionLayer({
          textureType: usingTextureArray ? 'texture-array' : 'texture',
          space: refSpace, stencil: false });
        session.updateRenderState({ layers: [proj_layer] });

        session.requestAnimationFrame(onXRFrame);
      });
    }

    function onEndSession() {
      xrSession.end();
    }

    function onSessionEnded(event) {
      xrButton.setSession(null);
      xrSession = null;

      // In this simple case discard the WebGL context too, since we're not
      // rendering anything else to the screen with it.
      gl = null;
    }

    function onXRFrame(time, frame) {
      let pose = frame.getViewerPose(xrRefSpace);
      xrSession.requestAnimationFrame(onXRFrame);

      scene.drawXRFrame(frame, pose);
      
      scene.endFrame();
    }

    initXR();
  </script>
</body>

</html>
